A small thing, but I just noticed that Quad snap doesn’t work on SubD edges.
I was able to work around it to do what I needed to do by using _DupEdge and using the quad snap on the edge.
Why do we need Quad snap to work on SubD edges? The same reasons Quad snap is useful on curves.
First and foremost: The extreme point of a subD object isn’t always at a vertex, so for precisely measuring and adjusting something like the depth of a hole or a depression in a SubD object, we need Quad snap.